1. Field of the Invention
The present invention relates to a coding method and a coder of a digital-video home system codec system for recording/reproducing a high-definition picture and a high-fidelity sound.
2. Description of the Prior Art
Since digital television broadcasts have begun to be on the air using MPEG2 (Moving Picture Experts Group 2) in 1994, many broadcasting companies all over the world are putting the digital broadcasts into operation or plan to put it into operation before long. The reason broadcasting companies participate in the digital broadcasts is that digital data has a trifling loss of information and provides both a high-quality moving picture and a high-fidelity sound, and that digital information has a compatibility which is well-suited for the multimedia age. At this time, many overseas electronics manufacturers anticipate the marketability of a digital data recorder (hereinafter, referred to as "DR") while they intensively invest their money in the development of DR's.
Victor Company of Japan, Ltd. (JVC) has finalized the technical specifications of a Digital-Video Home System (hereinafter, referred to as "D-VHS") Standard (STD) mode. Standardization of the specifications was achieved after consultation with Hitachi, Ltd., Matsushida Electric Industrial Co., Ltd. and Philips Electronics N.V. regarding D-VHS, which was announced in April of 1995. This paves the way for D-VHS technology to be incorporated in products, further advancing VHS as a recording medium in the upcoming multimedia age.
D-VHS is a new technology which is based on VHS, the world's most popular home video format. In addition to offering the features of the conventional VHS, to address the needs of multimedia applications, this new VHS technology offerers bit stream recording capability which will allow recording of compressed digital data such as digital broadcasts. By making the most of the advantages of tape media--namely high capacity and low cost--expectations are that D-VHS can be used in new applications, including in an in-home digital data storage device.
The digital broadcast has the video/audio characteristics of multichannel, high picture quality, surround sound, multilingual and so on. Also, in the aspect of information, the digital broadcasts are divided into service information such as program lists and commentaries, and data broadcasts such as PC softwares, shopping catalogs and electronic publishing. Technology which offers both recording and reproducing of a large quantity of diversified information is essential in the rapidly-progressing multimedia age. FIG. 1 is a block diagram for showing a schematic circuit configuration of a system for recording/reproducing digital broadcast data by a conventional D-VHS. As shown in FIG. 1, an audio/video signal which is supplied from a camera 11 is converted into a digital signal by an analog-to-digital converter 12 in a broadcasting station. The audio/video signal which is converted into a digital signal passes through a digital compressor 13 and is processed by a digital picture compression process such as the MPEG2. The compressed signal is QPSK (Quadrature Phase Shift Keying)-modulated by a modulator 14 and is propagated via a broadcast satellite 15. The digital broadcast data which is received by a broadcast receiving antenna 16, sequentially passes through a tuner 171 and a demodulator (not shown) and becomes a demultiplexed digital data. The demultiplexed digital data passes through an IEEE1394 digital interface and is provided to an input port of a D-VHS system 18 in the form of bit stream. The bit stream is recorded, in the format of a track, on a tape which is loaded on a deck (not shown) of D-VHS system 18.
In playback, the digital data which is read out from the tape passes through the IEEE1394 digital interface and is processed by a digital expander 172. The digital data from digital expander 172 passes through a digital-to-analog converter 173 and is provided to a television receiver 19.
Namely, bit stream recording is a method of recording compressed or processed, e.g., encrypted, signals such as those of digital broadcasts on a tape directly as digital data, and outputting them in the same state as they were input.
Therefore, a bit stream recording unit does not incorporate functions like analog-to-digital conversion, digital-to-analog conversion, digital compression/decompression or descrambling. Thus, video and audio signals cannot be reproduced using that unit alone. To reproduce the video and audio signals, the bit stream data must pass through a digital broadcast receiver's circuits that convert the digital data to video and audio signals.
Also, the D-VHS has the following characteristics. Firstly, in addition to analog recording of current broadcasting systems such as NTSC or PAL, timeshifting of digital broadcasts by bit stream recording is possible. Secondly, by offering the high-capacity characteristics of tape media, data recording in step with the multimedia age is possible. Thirdly, by maintaining compatibility with the current VHS format, playback of the vast VHS software library existing worldwide is possible. Fourthly, by utilizing most of the conventional VHS technology, parts and production facilities, widespread penetration and development for home use is possible.
The D-VHS has the recording capability of storing digital data for up to 7 hours at the input data rate of 14.1 [Mbps]. In a long play mode, the D-VHS has the recording capability of storing digital data for up to about 14 hours at the input data rate of 7 [Mbps]. Namely, the D-VHS has the recording capability of 44 [gigabytes]. The D-VHS is applicable to video servers, security recorders, data loggers, data storages and so on.
In step with the rapidly-progressing multimedia age, it is required to develop a coding method and a coder of a D-VHS codec system which performs an enormous quantity of computation in real time and has a low unit cost of manufacturing in order to store compressed information such as digital broadcast data in high capacity and to reproduce a high-definition picture and a high-fidelity sound.